186 REINFORCED CONCRETE CONSTRUCTION 



Hence, from equation (2), 



p = 1.7 per cent 



Illustrative Problem. What sectional area of vertical steel will be 

 required for a round column limited to 35 in. diameter, which has to bear 

 750,000 lb.; working stresses as recommended by Joint Committee? 



Using 1 per cent of bands or spirals, a pressure of 650 lb. per square inch 

 may be allowed on the concrete and 9750 lb. per square inch on the steel.- 

 One and one-half inch will be considered a sufficient protective covering 

 for the hooped reinforcement. Taking the area within the hooping as 

 effective, the safe strength of a corresponding plain concrete column would be 



^(650) =^^(650) =523,000 lb. 



Hence, from equation (2), 



P 750 



P' = 523 = 1 + (15 - 1)P 



/> = 3.1 per cent 



PROBLEMS 



60. What will be the safe strength of a column with a 12-in. Xl2-in. 

 effective cross-section, which is reinforced with 1.3 per cent of vertical 

 steel, the working stress in the concrete being 450 lb. per square 

 inch? Taken = 15. 



61. The effective area of a column is 196 sq. in. and the load to be carried 

 is 120,000 lb. What percentage of vertical steel is required if stresses as 

 recommended by the Joint Committee for a 2000 concrete are employed? 



62. Determine the size of square column, reinforced with 2 per cent of 

 longitudinal steel, which will be required to support a load of 100,000 

 lb. Provide protective covering for steel, and use the working stresses 

 as recommended by the Joint Committee. 



63. Find the diameter of a round column, reinforced by 1 per cent of 

 hooping, designed to support a load of 150,000 lb.; stresses as recom- 

 mended by the Joint Committee. 



64. Determine the required area of a column 15 ft. high, supporting 

 800,000 lb., and reinforced with 3 per cent of longitudinal steel and 

 1 per cent of hooping; working stresses as recommended by the Joint 

 Committee. 



65. What sectional area of vertical steel will be required for a round 

 column limited to 30 in. diameter, which has to bear 500,000 lb.? 

 Use the working stresses recommended by the Joint Committee. 



